mollusca

Question 1

Mollusca characteristics

Answer 1

• Second biggest group of marine organisms
• Fossilise well
• adapted to every kind of habitat in marine systems
• Most abundant class = gastropods, bivalvia

Question 2

Mollusca physical characteristics

Answer 2

• ventral
• dorsal
• mantle
• radula

Question 3

what is the ventral in molluscs

Answer 3

muscular foot
- contains nervous units
- can be used for swimming, digging, holding on, or capturing prey; missing only in Caudofoveata)

Question 4

what is the dorsal in molluscs

Answer 4

visceral mass containing internal organs

Question 5

what is the mantle in molluscs

Answer 5

• sheet of tissue covering all or part of the body -> creates a space between it and the visceral mass (mantle cavity) - includes epidermis secreting the calcium carbonate shell

Question 6

what is the radula in molluscs

Answer 6

• rasping organ containing a ribbon of chitin covered in rows of backwards-facing teeth with a moveable, fleshy base
• as teeth wear out, they are replaced by new rows from behind (lack in all bivalves and some gastropods)
• can be heavily modified

Question 7

what type of circulatory system do molluscs have

Answer 7

• Open circulation (except cephalopods)
• blood travels freely in spongy sinuses which surround it

Question 8

class gastropods characteristics

Answer 8

• All snails and slugs
• Head usually well-developed, with sensory appendages
• Large, muscular foot
• All show, to some degree, torsion – body has twisted so that the anus is now above the head

Question 9

2 different types / subclasses of gastropods

Answer 9

1. Prosobranchs
2. Opisthobranchs (all have reduced shell)

Question 10

Prosobranch characteristics

Answer 10

e.g. abalone, littorinids, whelks, heteropods
- Vast majority of marine snails (include heteropods)
- Mostly herbivorous - although some carnivores
- Important grazers e.g. macroalage - live on their food source
- Feed using radula

Question 11

what are heteropods

Answer 11

• ancient group of pelagic snails
• Usually warm water
• Foot is a laterally flattened, ventral fin
• Shell generally reduced or absent
• Active carnivores
• Telescopic eye – may be better than a fish’s

Question 12

orders within Opisthobranch

Answer 12

• Order Thecosomata - shelled pteropods
• Order Gymnosomata - naked pteropods
• Order Nudibranchia - sea slugs
  gills usually absent - exchange gas across body surface

Question 13

Order Thecosomata characteristics

Answer 13

• Foot modified into pair of wings to move
• Suspension feeders
• Trap food particles in mucous covered parapodia /mucous nets
• Play important ecological role – produce membrane bound faecal pellets that sink fast / export carbon to deep ocean when they die – help with ocean acidificaton

TGN

theco = thick (shelled)

Question 14

Order Gymnosomata characteristics

Answer 14

• naked pteropod - Lack shell and mantle cavity
• Streamlined, pair of wings near head
• Hooks, teeth and adhesive tentacles (cephaloconi) or Tentacle bearing suckers (acetabula)

Question 15

Order Nudibranchia characteristics

Answer 15

• Bilaterally symmetrical (secondary detorsion)
• Grazing carnivores
• Feed on sessile organisms e.g. corals, sponges
• Each family restricted to one type of prey
• Dorsal surface often has projections called cerata (Involved in gas exchange)

Question 16

what do molluscs with no shell use for defence e.g. Gymnosomes and Nudibranchia

Answer 16

• Primary motor of defence = camoflage
• Chemical defence = toxins (synthesised by the slug / taken from prey – stolen nematocysts = kleptocnidae)

Question 17

family conidae characteristics e.g dog whelk

Answer 17

• Cone shells
• Ones that eat fish have hollow harpoon connected to venom gland – contain neurotoxins to kill the fish

Question 18

dog whelk characteristics (family conidae)

Answer 18

• mainly barnacles and mussels, also other bivalves and gastropods
• Important intertidal predator
• Mouth and radula on an extensible proboscis - radula modified to bore holes in shells
• Accessory Boring Organ on the sole of the foot secretes a shell -softening chemical
• Once penetrated, the prey is narcotised before the whelk secretes digestive enzymes into the body of the prey - then ingests the resultant tissue ‘soup’

Question 19

class bivalve characteristics

Answer 19

clams, oysters, mussels, etc.
- Shell of two halves (valves) - hinged dorsally by calcified teeth + tough ligament which springs the shell open / Shell held closed by adductor muscles
- Dominated by lamellibranchs
- siphons in burrowing species
- Muscular foot often used for digging
- Large gills (ctenidia) - gas exchange + food collection

Question 20

blue mussel characteristics (class bivalve)

Answer 20

Foot is reduced and used to attach byssal threads to substratum

Question 21

Class Polyplacophora (chitons) characteristics

Answer 21

• Ovoid / dorso-ventrally flattened
• Shell divided into 8 overlapping plates
• Use foot to move like a snail
• Commonly intertidal
• Move and feed at high tide
• Gills for gas exchange

Question 22

what are the large gills called in bivalves

Answer 22

ctenidia

Question 23

what are stollen nematocysts called

Answer 23

kleptocnidae

Question 24

what are the tentacle characteristics called that Order Gymnosomata have

Answer 24

adhesive tentacles (cephaloconi) or Tentacle bearing suckers (acetabula)